Variable electric impedance



Jan. 10, 1961 DE GIER 2,967,945

VARIABLE ELECTRIC IMPEDANCE Filed Nov. 13, 1958 Iiiii) "III/l INVENTORmcO ARIE OE GIER AGENT United States Patent VARIABLE ELECTRIC IMPEDANCENico Arie De Gier, 'Eindhoven, Netherlands, assignor to North AmericanPhilips Company, Inc., New York, N.Y., a corporation of Delaware FiledNov. '13, 1958, Ser. No. 773,764

Claims priority, application Netherlands Mar. 9, 1957 7 Claims. (Cl.250-217) This application is a continuation in part of application S.N.718,322, filed Feb. 28, 1958.

This invention relates to variable electric impedances and moreparticularly variable resistances. Variable resistors are frequentlyused in electrical engineering and in their known type the resistance isregulated by mechanical means by sliding a contact along the resistorbody. A known disadvantage of this design is inter alia that, due tocontact phenomena on the sliding contact, more particularly in the end,so-called crackling or heavy noise occurs.

The invention has for its purpose inter alia to mitigate thisdisadvantage and it provides a particular type of such a device which isfundamentally diiferent and the impedance of which may be regulatedelectrically in a simple manner.

A variable electric impedance according to the invention comprises astructural combination of a radiationsensitive body on which at leasttwo electrodes determining the impedance are provided and an adjustablesource of radiation for regulating the impedance. The source ofradiation and the radiation-sensitive body are preferably united by acommon envelope to form a structural unit. If necessary, the commonenvelope may also serve as a protection against unwanted externalradiation which influences the radiation-sensitive body in aninterfering manner. In addition, the radiation-sensitive body and thesource of radiation preferably each have a separate envelope and boththese envelopes are united into a structural unit. The manufacture ofsuch a device is thus considerably simplified and this embodiment alsohas the advantage that the two systems. cannot influence each otherchemically.

In one particular embodiment according to the invention, the envelope ofthe radiation-sensitive body also serves as a support for the envelopeof the source of radiation. The two envelopes in this case consist, atleast in part, of material permeable to radiation. The source ofradiation comprises, for example, an ordinary small incandescent lamp(filament and glass bulb) or a small gaseous discharge tube, for examplea neon lamp. By regulating the current and/or voltage through the sourceof radiation, the intensity of the radiation and hence the impedancebetween the two electrodes on the semiconductive body is varied. Theradiation-sensitive body comprises, for example, a photo-resistance,preferably a thin sintered symmetrically-conductive cadmiumsulphide discprovided with an interdigital system of line electrodes. As analternative, the radiation-sensitive body may be, for example, aphoto-sensitive blockinglayer system, such as a photo-diode or aphoto-transistor, or a photo-electric cell having an internal blockinglayer (p-n transition).

It is to be noted that it was known to utilise a radiation-sensitivebody in conjunction with a source of radiation, for example in guardinstallations, the variation in impedance between the electrodes of theradiation-sensitive body which occurs when the radiation path between2,967,945 Patented Jan. 10, 1,961

the radiation-sensitive body and the source of radiation is interruptedbeing used as the alarm signal. However, in this case, the source ofradiation and the radiationsensitive body are used as elementsstructurally separated. The particular possibilities concealed in such acombination as a variable electric impedance, more particularly asvariable electric resistance, are accentuated by the step according tothe invention and also a large-scale use is made possible in a simpleand, in practice, serviceable and eflicacious manner.

In order that the invention may be readily carried into eifect, severalembodiments will now be described in detail, by way of example, withreference to the accomr panying drawings, in which:

Fig. la is a longitudinal section of one particular embodiment of thedevice according to the invention;

Fig. 1b is a bottom view of the hardpaper plate 6 of a modification of adevice according to the invention;

Fig. 2 is a plan view of the radiation-sensitive body used in the deviceof Fig. 1;

Figures 3 and 4 are sectional views of further embodiments of devicesaccording to the invention.

The embodiment of a variable electric impedance according to theinvention shown in Fig. 1 is particularly suitable and simple instructure. At right angles to the plane of drawing, the assembly issubstantially circularsymmetric. The radiation-sensitive body 1comprises a thin disc of sintered cadmium-sulphide powder activated withcopper and gallium. On its upper side, the disc is provided with aninterdigital system of line electrodes comprising two comb-likeelectrodes 2 and 3, as shown in detail in Fig. 2. Within the scope ofthe invention, it is naturally also possible to provide more than twoelectrodes on the disc, for example by dividing one comb-like electrodeinto two or more separate parts. The cadmium-sulphide disc has adiameter of, for example, about 8 mms. and a thickness of about 0.5 mm.The line electrodes consist, for example, of aluminum provided byevaporation, the distance between the electrodes being, for example,several tenths of a millimetre. The resistance between the electrodes,without illumination or with weak illumination only is, for example, 10

megohms, whereas the resistance may have decreased to less than 500 ohmswith strong illumination, for example 15,000 luxes. It will be evidentthat much variation in said values is possible by suitable choice of theradiation-sensitive substance and the activation thereof. Theradiation-sensitve body 1 is housed in a separate boxlike glass envelope4, and this preferably directly under its flat upper side 5. In order toprovide good protection of the radiation-sensitive layer 1 againstmoisture and the like and to ensure good mechanical rigidity of theassembly, the radiation-sensitive body 1 is glued on a thin plate 6 ofhardpaper, the lower side of the envelope being properly sealed byfilling the remaining space 7 with cast resin. Supply leads 8 and 9 areconnected to the comb-like electrodes 2 and 3, for example, with the aidof a silver paste. The variable source of radiation 10 comprises anordinary small incandescent lamp (6.3 volts; 0.1 amp.), the glass bulb11 of which is locally glued in position on the flat upper side of theenvelope 4 for the radiation-sensitive body 1. At the area of thejunction between the two envelopes, the bulb 11 has a substantially flatsurface. This considerably simplifies the assembly and results in aconsiderable increase in radiation intensity because of the resultantsmaller distance between the filament 12 and the radiation-sensitivebody 1. Due to their junction, the two envelopes are united into astructural assembly, the envelope for the radiation-sensitive body alsoserving as a support for the envelope of the source of radiation. Theassembly is also housed in a'small aluminum tube- 13 impermeableto-radiation; t-h'e upper and lower sides of which are closed 30 bymeans of a suitable insulating material, for example hardpaper.Protection against interfering radiation from without may alternativelybe provided by covering the assembly with an opaque lacquer layerinstead of using the common envelope. The supply leads 31 of theincandescent lamp are led to the exterior at the upper side and thesupply leads 8 and 9 at the lower side. The intensity of radi- 'ationand hence also the resistance between the two electrodes 8 and 9 may bevaried over a large range by regulating the current and/or voltagethrough the filament 12.

In certain cases in which, instead of a gradual variation in resistancethroughout the range, a more abrupt transiton is desired, then accordingto a further aspect of the invention it is possible to use with muchadvantage a "small gaseous discharge tube instead of an incandescentlamp in structurally the same manner, which gaseous "discharge tube isnot ignited until at a given threshold voltage, so that the resistanceof the radiation-sensitive body is suddenly decreased drastically andmay, if desired, be regulated back a little further above the thresholdvoltage. For this purpose, use may be made, for example, of neon tubes,which are commercially sold.

Fig. 3 shows a longitudinal section of another embodiment of the deviceaccording to the invention, in which the source of radiation may bereplaced, if desired. For this purpose, the source of radiation 10 issecured in a fitting 15, which is detachably arranged in an envelope 13'common to the source of radiation 10 and the photoconductive layer 1.The common envelope 13' consists of plastic material, which istransparent, and has a partition 16. The radiation-sensitive body 1 ishoused in the space under the partition 16, without using a separateenvelope, in the same manner as shown in Fig. l. The fitting 15 may beslid out of the upper space of envelope 13 and is kept in position bymeans of two resilient strips 17, 18 which engage in two grooves of thefitting. The strips 17, 18 also serve as supply conductors for thesource of radiation. The envelope 13' is externally provided with anopaque layer '19.

It has been found in practice that the possibility of replacement of theincandescent lamp is not absolutely necessary and that variableresistances as shown in Fig. 1 may be manufactured with a very long lifeby using a source of radiation having a long life per se, for examplebecause of the comparatively low temperature of its filament, and alsoby subjecting the source of radiation to a load lower than normal.

Fig. 4 shows again another embodiment of a variable resistance accordingto the invention. In this case, the source of radiation comprises asmall gaseous discharge tube, that is to say a neon tube 10". Aninterdigital system 29 of line electrodes is first provided on the upperside of the bulb and on top 'of the electrode system there is sprayed aphoto-sensitive layer 1, which consists of a mixture of organic binderand CdS-powder. The assembly is surrounded by an opaque lacquer layer28.

It will be readily evident that for an expert it is possible to applynumerous structural modifications in this variable impedance within thescope of the invention. Thus, for example, it is possible for theincandescent lamp in the construction shown in Fig. 1 to be secured at aside wall of the bulb to the envelope of the radiation-sensitive bodyinstead of at its top. The common envelope may internally be provided,for example, with a highly reflecting layer. The bulb of the source ofradiation may be shaped so, and internally be provided in part with areflecting layer so, that the radiation is concentrated to theradiation-sensitive layer.

The variable impedance according to the invention is suitable for use inall kinds of circuits. In this case it is an advantage that theregulating circuit including the source of radiation may be galvanicallyseparated from the circuit to be regulated which includes theradiation-sensitive body. Another advantage of a variable resistanceaccording to the invention is that, due to the inertia of the source ofradiation, it is free from noise or crackling, even though theregulating members in the regulating circuit are not. Another advantageis the simple possibility of remote control which considerablysimplifies its incorporation in equipment. The variable impedance may bearranged in the equipment at an area which is optimum electronically,whereas the members for regulating the circuit of the source ofradiation may be arranged in the equipment at the area which is simplestin mechanical respect, if desired at a distance of many metres from thevariable impedance according to the invention.

The variable impedance according to the invention is very suitable, forexample, for use in so-called potentiometer circuits. For this purpose,a fixed resistor is included in the circuit in series with the radiationsensitive body, the total voltage being applied to this scries-combination, while the partial voltage to be controlled is derived betweenthe two electrodes of the radiationsensitive body and the electriccontrol signals are sup plied to the source of radiation. Forapplications in which a fixed resistor is used in combination with theradiation-sensitive body, according to a further aspect of theinvention, the resistor may be included in a simple manner in thestructural unit comprising the source of radiation and theradiation-sensitive body, for example as indicated in Figure lb. Such adevice may be quite similar to the one shown in Figure la except thedetails shown in Figure lb. In order to include the fixed resistor inthe structure, the hard paper plate 6 has been provided at thebottomside, shown in plan view in Figure lb, with a thin resistancelayer 22 by a known technique with the aid of a carbon suspension, athird electrode 20 similar to electro es 8 and 9 has been added, whichis connected with the carbon layer 22 in the way indicated by means of asilver paste layer 21, while the other end of the carbon layer 22 hasbeen connected with the electrode 9 also by means of a thin silver pastelayer 21.

In conclusion, a particular effect is mentioned which may be obtainedwith a variable impedance according to the invention, the source ofradiation of which comprises a small incandescent lamp and theradiation-sensitive body of which comprises a photo-resistance ofcadmium sulphide, more particularly sintered cadmium sulphide, activatedwith Cu and Ga, each about l0 gram-atom per gram-molecule of CdS. Forthis purpose, the device is included in a circuit, a linearly-variableresistance being included in series with the filament of theincandescent lamp. It has been found that the impedance of thephotoresistance as a function of the angle of rotation of thelinearly-variable resistance connected in series with the lamp shows alogarithmic course. Such a combination according to the invention thuspermits of obtaining a logarithmic-variable resistance in a simplemanner.

What is claimed is:

l. A variable-impedance electrical device comprising an electrical lampincluding an envelope and a filament whose voltage determines its outputlight intensity, a hollow, optically-transparent body secured to thelamp envelope, a support member, a photo-conductive member mounted onthe support, a thin fixed-resistance member mounted on the support andconnected to the photo-conductive member, said support being mountedwithin the hollow body with the photo-conductive member oriented toreceive directly the light radiated by said lamp, an opaque elementsurrounding the lamp envelope and hollow member, and a pair ofelectrodes coupled to spaced points of the pho'toconductive member.

2. As a new variable-impedance circuit component, the combinationcomprising an electrical lamp including an envelope and a filament whosevoltage determines its output light: intensity, a hollow,optically-transparent body secured to the lamp envelope, asymmetricallycOnductiVe, photo-conductive member mounted within thehollow body to receive directly the light radiated by said lamp, anopaque element surrounding the lamp envelope and hollow member, aninterdigital system of line electrodes coupled to spaced points of thephotoconductive member, and external terminals on the componentconnected to the lamp filament and the line electrodes.

3. A component as set forth in claim 2 wherein the photo-conductivemember comprises a sintered layer of cadmium sulphide.

4. A component as set forth in claim 2 wherein the hollow membersupports the lamp envelope.

5. As a new variable-impedance circuit component, the combinationcomprising an opaque housing, a hollow glass body within the housing, alayer of photo-conductive material on the inside surface of a wallportion of the hollow glass body, an electrical lamp within the housingand comprising a glass envelope secured to the outside surface of saidwall portion of the hollow glass body and opposed to thephoto-conductive layer and electrode means within the lamp envelope forgenerating radiation in response to an exciting voltage applied to theelectrode means, a pair of electrodes coupled to spaced points of thephoto-conductive layer, and separate external terminals on the componentinternally connected to the lamp electrodes and the electrodes coupledto the photo-conductive layer.

6. A circuit component as claimed in claim 5 wherein the said wallportion of the hollow glass body is flat, and t the lamp envelope has aflattened portion joined thereto.

7. As a new variable-impedance circuit component,

the combination comprising an electrical lamp including an envelope anda filament whose voltage determines its output light intensity, ahollow, optically-transparent body secured to the lamp envelope, asymmetrically-conductive, photo-conductive member mounted within thehollow body to receive directly the light radiated by saidlamp, anopaque element surrounding the lamp envelope and hollow member, a pairof electrodes coupled to spaced points of the photo-conductive member,and external terminals on the component connected to the lamp filamentand the pair of electrodes.

References Cited in the file of this patent UNITED STATES PATENTS

